RESUMEN
Effects of the local anaesthetic trimecaine and its quaternary derivative on the isolated rat sciatic nerves were examined. Trimecaine inhibited action potential propagation in the isolated nerve in vitro at four-times lower concentrations than its quaternary derivative. Despite extracellular application, the quaternary derivative inhibited action potential propagation in the sciatic nerve but with a longer half-life in comparison with trimecaine. With increasing external pH, the blocking effect of trimecaine was profound. The blocking potency of the quaternary compound was not consistently changed with the changes in external medium pH.
Asunto(s)
Anestésicos Locales/farmacología , Nervio Ciático/efectos de los fármacos , Trimecaína/análogos & derivados , Trimecaína/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Técnicas In Vitro , RatasRESUMEN
Sodium channel blocking activity was measured in a series of newly synthesized tertiary amine compounds and their quaternary derivatives applied externally on internally in the rat sensory neuron. The large difference in effectiveness of the quaternary compounds on external and or internal application became smaller and even disappeared with increasing lipophilicity of the compounds. No such difference was observed in the tertiary analogs. It was concluded that lipophilicity played an important role in determining the channel blocking activity of externally applied quaternary compounds. The results suggest that, in addition to the neutral form, highly lipophilic amine local anesthetics may penetrate into and/or pass across the neuronal membrane probably as electroneutral ion pair complexes consisting of the cationic form and an appropriate anion. The present results support our hypothesis which stresses, in addition to dissociability, the role of lipophilicity of amine local anesthetics in the pH dependence of their effect.
Asunto(s)
Anestésicos Locales/farmacología , Neuronas/efectos de los fármacos , Anestésicos Locales/análisis , Animales , Carbamatos/farmacología , Fenómenos Químicos , Química Física , Diálisis , Difusión , Técnicas In Vitro , Lípidos/análisis , Ratas , Canales de Sodio/efectos de los fármacos , Solubilidad , Trimecaína/farmacologíaRESUMEN
A modification of the technique of intracellular dialysis of isolated single excitable cells, such as rat spinal ganglion neuron, suitable for potential clamping of its somatic membrane is described. The advantage of the new modification is the substantial reduction of the effect of inherent resistance in series (RS) to the membrane resistance (RM) on precision of potential clamping. This is attained by reversal of cell position in the perfusion pipette resulting in an approximately tenfold reduction in the area of active membrane. The resistance of this area proportionally increased while RS remained unchanged. Hence the error in potential fixation, which is inversely proportional to the ratio RM/RS, is by approximately one order smaller with the new technique than with the original one. An essential step in the new technique is the osmotic expansion of the cell to improve the contact of the cell with the perfusion pipette in the pore and to facilitate disruption of the appropriate part of the membrane. All features and advantages of the technique of intracellular dialysis, such as simplicity, the possibility to easily change ionic composition of media, and/or to apply drugs to any side of the membrane in the same cell, etc., have been maintained.